The method is often limited to surface cancers due to the
low penetration of light through biological tissue. The NUS team’s approach
involves the insertion of a tiny wireless device at the target site, extending
the spatial and temporal precision of PDT deep within the body.

Researchers at the National University of Singapore have developed
a novel approach for using a powerful light-induced cancer treatment for inner
organs of the body. The method is often limited to surface cancers due to the
low penetration of light through biological tissue.

Photodynamic therapy
(PDT) uses a light sensitive drug, called a photosensitiser, that is
triggered by a specific wavelength of light, to produce a form of oxygen that
kills nearby cells. This provides a precision approach to cancer therapy,
avoiding many of the whole-body side effects of classical drugs such as
chemotherapy. In addition to directly killing cancer cells, PDT shrinks or
destroys tumours by damaging blood vessels in the tumour, preventing the cancer
cells from receiving necessary nutrients. PDT may also activate the immune
system to attack the tumour cells.

Traditional light sources such as light-emitting diodes
(LEDs) or lasers may be used for surface tumours, such as skin cancer, but the
low penetration of light through tissue limits the depth to less than a
centimetre. An endoscope – a thin, lighted tube used to look at tissues inside
the body – can be used to insert a fibre optic cable into the inner lining of
some organs, such as the oesophagus. But for organs such as the brain or liver,
the organ must be exposed by surgery before PDT can be used.

The new wireless approach of light delivery enables PDT to
be used on the inner organs of the body with fine control.

The study, supported by the Singapore Ministry of
Education’s Tier 3 grant, was led by Professor Zhang Yong and Assistant
Professor John Ho, who are from the Department of Biomedical Engineering and
Department of Electrical and Computer Engineering at NUS Faculty of Engineering,
respectively. The findings of the study were published in the scientific
journal Proceedings of the National Academy of Sciences (PNAS) on
29 January 2018.

The NUS team’s approach involves the insertion of a tiny
wireless device at the target site, extending the spatial and temporal
precision of PDT deep within the body.

The miniaturised device, which weighs 30 mg and is 15 cubic mm in
size, can be easily implanted, and uses a wireless powering system for light
delivery. A specialised radio-frequency system wirelessly powers the device and
monitors the light-dosing rate after the device has been implanted at the
target site.

The team demonstrated the therapeutic efficacy of this
approach by activating photosensitisers through thick tissues – more than three
centimetres – which are inaccessible by direct illumination, and by delivering
multiple controlled doses of light to suppress tumour growth.

Asst Prof Ho said, “Our approach of light delivery will
provide significant advantages for treating cancers with PDT in previously
inaccessible regions. Powered wirelessly, the tiny implantable device delivers
doses of light over long time scales in a programmable and repeatable manner.
This could potentially enable the therapies to be tailored by the clinician
during the course of treatment.” Asst Prof Ho is also a Principal Investigator
at the Biomedical Institute for Global Health Research and Technology
(BIGHEART) at NUS.

“This novel approach enables ongoing treatment to prevent
reoccurrence of a cancer, without additional surgery. The application of the
technology can also be extended to many other light-based therapies, such as
photothermal therapy, that face the common problem of limited penetration
depth. We hope to bring these capabilities from bench to beside to provide new
opportunities to shine light on human diseases,” said Prof Zhang.

The team is now working on developing nanosystems for
targeted delivery of photosensitisers. They are also coming up with minimally
invasive techniques for implanting the wireless devices at the target site and
looking into integrating sensors to the device to monitor the treatment
response in real-time.

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